The present invention relates to an aircraft air conditioning system and method, and more particularly to an apparatus and method for controlling the climate in the passenger cabin of an aircraft enclosure.
For many years the provision of air conditioning systems, as well as heating systems, has been known and advanced in the aircraft industry. In particular, it is known to supply a relatively constant flow of fresh air into the pressurized body of commercial aircraft both on the ground and in the air for ventilating the passenger cabin, the cockpit, and other pressurized regions within the aircraft. In order to maintain a relatively constant and comfortable temperature and humidity level of the ventilation air for the passengers and crew in the aircraft, recirculation air from the cabin area of the aircraft typically is mixed with fresh air.
Conventional air conditioning systems for commercial aircraft often use open loop systems to provide a mixture of fresh air and recirculated air into the pressurized compartment. An example of a conventional aircraft air conditioning system is shown in FIG. 1. According to FIG. 1, the conventional air conditioning system 10 comprises several components, most of which are located in the pressurized compartment 40 of the aircraft. In operation, fresh air is provided by fresh air treatment hardware, such as air conditioning packs 30, located in the unpressurized area 50 of the aircraft. The recirculation air 12 from the pressurized compartment 40, such as the passenger cabin, cockpit, and selected cargo areas, is first processed through a filter 14 and then delivered by fans 16 to be mixed with the fresh air from the packs 30 prior to distribution to the pressurized compartments.
In conventional high cooling capacity systems 10, the mixing of sub-freezing fresh air and recirculated cabin air 12 occurs in a large mix manifold 20 located in the pressurized compartment 40, which thereby disadvantageously reduces the amount of available pressurized space in the aircraft. In large aircraft, the mix manifold 20 and associated ducting may take up to about 400 ft3. The mix manifold 20 is also used to remove entrained moisture, such as ice particles or water droplets, from the air mixture and to prevent ice from propagating into the passenger cabin or crew areas via air distribution ducting 22. Conventional air conditioning systems also include a check valve 34 in line with the pack conditioned air supply lines 32 and 36 that delivers the fresh air from the packs to the mix manifold 20. The check valve 34 protects against depressurization of the pressurized compartment due to a rupture in the pack conditioned air duct 32 in the unpressurized area 50.
Some smaller commuter-type aircraft include a mix manifold in the unpressurized area proximate to the air conditioning packs. However, cabin depressurization is not a concern with these types of aircraft because they typically operate at low altitudes. Therefore, check valves and/or shutoff valves in the conditioned air supply line and distribution ducting are not required.
The air conditioning packs 30 that provide cold fresh air often carry ice suspended in the air stream, particularly when the aircraft operates at hot, humid, and low altitudes. Conventional methods of air mixing in the mix manifold 20 unfortunately allow the ice particles to combine into larger particles. As such, it may be relatively difficult to melt the ice prior to its introduction into the air distribution ducting 22. This often results in or contributes to several known problems, such as clogging of the distribution ducting, noise, and a condition known as xe2x80x9csnow in the plane,xe2x80x9d wherein ice particles are distributed through the distribution ducting 22 and into the passenger cabin or crew areas. Several systems have been developed to address these problems. One such system provides a recirculation heat exchanger unit downstream of the mix manifold to melt any ice suspended in the air stream. The system also includes an ice sensor adapted for controlling a valve and directing a flow of warm air into the air steam to melt any ice suspended therein.
However, conventional aircraft air conditioning systems, including those mentioned above, continue to suffer from several disadvantages. In particular, conventional air conditioning systems occupy pressurized space, which could otherwise be used for passengers or cargo. In addition, conventional air conditioning systems typically include a mix manifold, which adds to the weight of the aircraft, contributes to the noise level in the passenger compartment, and requires extensive development testing. It would be desirable, therefore, to provide an aircraft air conditioning system that is lighter and quieter and that does not occupy as much space within the pressurized compartment of the aircraft.
These and other needs are provided, according to the present invention, by an aircraft air conditioning system and method that is highly efficient, lightweight, and designed to directly mix recirculated cabin air with fresh air without requiring a mix manifold in the pressurized compartment of an aircraft. As such, the present invention is particularly advantageous for large, commercial type airplanes. It should be noted, however, that the air conditioning system of the present invention is not limited to airplanes. Regardless of the type of aircraft, the air conditioning system and method is designed to reduce the noise level in the passenger cabin while also freeing up more room in the pressurized area for passengers, cargo, or equipment.
According to the present invention, the air conditioning system and method are adapted for use in an aircraft having a pressurized area and an unpressurized area separated by a pressure bulkhead. The air conditioning system includes one or more conventional air conditioning packs located in the unpressurized area of the aircraft, such as an underwing area.
The air conditioning system also includes a first air duct that extends between the pressurized area and the unpressurized area of the aircraft. The first air duct directs a flow of recirculation air from the pressurized area, such as a passenger cabin area and/or cargo areas, to the unpressurized area through the pressure bulkhead. In one embodiment, a fan is disposed in fluid communication with the first air duct to assist in directing the flow of recirculation air.
The air conditioning system also includes a mixer, operatively positioned in the unpressurized area downstream of the air conditioning pack, for mixing the conditioned air from the air conditioning pack and the recirculation air from the pressurized area. The mixer combines the two air flows into a resultant air mixture such that any ice present in the conditioned air is melted. Advantageously, the relatively small and efficient mixer of the present invention obviates the need for a mix manifold and saves valuable space for passengers, cargo and/or other aircraft equipment within the pressurized area. In addition, placement of the mixer in the unpressurized area can also reduce the noise in the passenger compartment relative to conventional designs.
The air conditioning system also includes a second air duct connected to the mixer that directs the resultant air mixture from the mixer back to the pressurized area of the aircraft. To protect against depressurization of the pressurized area, a check valve, such as a flapper valve or the like, is provided between the pressurized and unpressurized areas at the pressure bulkhead. A plurality of scuppers are provided in the second air duct for removing moisture from the resultant air mixture as the mixture travels through the second air duct. Advantageously, the mixer is designed to swirl the resultant air mixture, which allows the moisture in the resultant air mixture to condense into water droplets and be collected by the scuppers in the second air duct before the mixture is distributed into the pressurized area, thus substantially reducing the possibility of liquid or ice particles in the mixture. Moreover, since the water is condensed at the outlet of the air conditioning pack, more second air duct length is available to collect the water via the scuppers.
The air conditioning system also includes an aerodynamic shutoff valve in line with the first air duct at the pressure bulkhead and also adapted for protecting against depressurization of the pressurized area. More specifically, the aerodynamic shutoff valve provides protection of the pressurized area in the event of a duct rupture in the unpressurized area, yet allows the recirculation air to travel from the pressurized area to the unpressurized area. As discussed more fully below, the aerodynamic shutoff valve permits air to pass from the pressurized area to the unpressurized area under normal conditions, but closes when a predetermined pressure differential across the shutoff valve is exceeded. Thus, the pressurization of the passenger compartment is protected even as air is passed to and from the unpressurized area in order to be properly mixed.
A method of air conditioning an aircraft enclosure is also provided. The method includes providing a flow of recirculation air from the pressurized area to the unpressurized area, and then mixing the recirculation air with a flow of cooling air to form a resultant air mixture. The cooling air may contain suspended ice particles, but by mixing the cooling air with the warmer recirculation air, the suspended ice particles are melted or substantially eliminated into water droplets and collected within the second air duct that returns the resultant air mixture to the pressurized area. In this regard, the second air duct is adapted for removing moisture from the resultant air mixture, such as by including scuppers, and is operably connected to the pressurized area via a check valve, such as a flapper valve. As such, the resultant air mixture substantially reduces or eliminates small fog or ice droplets suspended in the air flow supplied to the passenger cabin area, cargo areas, and other pressurized areas.
Advantageously, the mixing occurs in the unpressurized area of the aircraft and without the use of a mix manifold. By doing so, the present invention provides an aircraft air conditioning system and method having less weight, less noise, and a more effective means of moisture removal, yet providing ease of maintenance. In addition, the passengers and crew of the aircraft enjoy a quieter flight because the mixer resides outside of the pressurized area. Moreover, locating the mixer of the present invention in the unpressurized area of the aircraft results in a larger percentage of the pressurized area that can be used for revenue production, such as passenger seating or cargo.